Ubuntu 20.04 brightness adjust not working

The xrandr solution didn't worked for me. I have installed brighness-controller and worked well.

sudo add-apt-repository ppa:apandada1/brightness-controller
sudo apt update
sudo apt install brightness-controller

UPDATED: After I have upgraded to Ubuntu 21, this issue has fixed completely. My laptop buttons of brightness control works normally. No needed additional configuration.

I am having similar issue. There is no screen brightness slider on system menu (the one below the volume). I know that there is a workaround using xrandr that goes like this:

xrandr -q | grep " connected"

The output looks like:

DP-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 477mm x 268mm
DP-3 connected primary 1920x1080+1920+0 (normal left inverted right x axis y axis) 477mm x 268mm

I am using a dual screen, so that is why I have 2 channels (DP-1 and DP-2). Then you can adjust the brightness by typing

xrandr --output DP-3 --brightness 0.8

Here, I am using 0.8 in monitor DP-3. Just do the same for the other monitor and we are all set.

However, I noticed that the screen brightness is oscillating and no solution that I found in the internet worked for me.

I had the same problem, which was solved following this post: How to Fix Brightness Keys Not Working in Ubuntu. The solution is quite simple:

1. Edit file /etc/default/grub and set:

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor acpi_osi=linux"
   

2. Save the file and update GRUB:

   sudo update-grub
   

3. Restart the computer and it worked.

The rational behind the operations, as the author explained, is as follows:

ACPI is a power interface management standard which is implemented in operating system kernels. By default Linux kernel uses an inbuilt driver for keyboard keys, which is often non compatible with some keyboards.

Hence, we specify the option acpi_backlight=vendor which tells the kernel to take precedence of vendor driver over kernel driver. The option acpi_osi=linux tells the kernel to enable inbuilt ACPI workarounds for Linux drivers; which can be the case if the device driver has issues for Linux architecture.

I had the same issue, in my case all answers I found not working. Maybe my case is specific, but I hope my answer can help someone.

My computer is a Lenovo Legion Y740-15I with a nvidia GeForce RTX 2060. I have tried all solutions available but none worked. One day by chance when I installed tensorflow I had to install CUDA Toolkit 11.0 and his compiler.

After CUDA installation and a reboot I noticed brightness controller is working !!! I gave you all steps I followed below :

1. Follow base installer instructions for CUDA nvidia toolkit (official release instructions)
2. Check CUDA version $ cat /usr/local/cuda/version.txt
3. Install CUDA compiler $ sudo apt install nvidia-cuda-toolkit
4. Check CUDA compiler version $ nvcc -V
5. Reboot computer
6. Check if nvidia driver communicate with GPU $ nvidia-smi If you can see CUDA Version: 11 installation is done !

Now check if your brightness controller work. Hope this might help someone...

PS: Also resolved boot black screen problem when login

In my case, I resolved this problem by upgrading the kernel version from 5.4 to 5.6. Run:

sudo apt-cache search linux-image-5

This will return the list of available kernels. I installed linux-image-5.6.0-1028-oem which is listed at the bottom at the moment.

You can install it as follows.

sudo apt install linux-image-5.6.0-1028-oem

After rebooting your system, you may see that your kernel is updated.

As a reference, my GRUB_CMDLINE_LINUX_DEFAULT is set to be that of the original one, i.e. GRUB_CMDLINE_LINUX_DEFAULT="quiet splash". In addition, I installed the brightness-controller, but I'm not sure whether it helped me or not.

Hope this might help you.

For me, the problem was solved by simply rebuilding the initrd another time after booting into the new kernel:

sudo dpkg-reconfigure linux-image-5.4.0-54-generic

Obviously, you should run this with the package of your current boot kernel. If you are unsure, run uname -r to get the kernel name. Moreover, package names after dpkg-reconfigure auto-complete in my bash, but your settings may vary.

Doing this should always be safe and quick, so it would not hurt to try this before you do anything else. However, I add more details on my setup and what else I did below.

My configuration and observed behaviour

• Problem was as described above, first found after upgrade to Ubuntu 20.04 (brightness worked before)
• Renato Miotto's solution (via xrandr --output ... --brightness 0.8) allowed me to change brightness, but system keys still do not work and using xrandr resets screen colour (night colour mode)
• Macbook Air 3,2 (very old, tends to have EFI boot issues related to graphics)
• KDE Neon, Nvidia video drivers, kernel 5.4.0-54-generic

Note that Nvidia drivers on MacBook Air 3,2 have a whole set of other, unrelated issues, some specifically related to brightness control. In particular, you need to add X-related device option settings EnableBrightnessControl=1 as per Brightness not working after installing NVIDIA driver. Also, MacBook Air 3,2 by default may fail to boot usable graphics altogether in Nvidia drivers, which is fixed by setting certain PCI-E registers in grub as per Proprietary NVidia drivers with EFI on Mac, to prevent overheating. Both were applied before on my machine and remained active after the upgrade, so not related.

What else I did (may have interacted with the above fix)

I saw two more boot-level issues after the upgrade and I fixed them too. Doing this might have interacted with the effectiveness of my fix:

1. I fixed Failed to Set MokListRT: Invalid Parameter by following (a KDE Neon adapted version of) Shibiwan's answer on Ubuntu 20.04 Failed to Set MokListRT: Invallid Parameter.
2. My grub boot menu had vanished too. I recovered it by editing /etc/default/grub to contain GRUB_TERMINAL=console, GRUB_TIMEOUT_STYLE=menu, and GRUB_TIMEOUT=10. After this, update-grub needs to be run (which the above dpkg-reconfigure will do as well).

Having the grub menu working is also a minimal safety net when tempering with boot settings, so it makes sense to address this first if you see this too.

1. Open the grub file from the directory /etc/default or run the command:

   gedit /etc/default/grub
   

   in a terminal.

2. Edit the following line from:

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
   

   to:

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash pcie_aspm=force acpi_backlight=native"
   

3. Run the command:

   sudo grub-update
   

4. Restart your computer.

I had much easier solution. Somehow unintentionally I've disabled "Handle display brightness keys" option in Xfce Power Manager. When pressing the brightness keys, the notification popup was displayed but the brightness bar wasn't moving. I took quite a while before I realized this.

However this is only related to XFCE, I have Xubuntu 20.04.

Hi new to this particular forum so don't yet have enough reputation to just leave a comment. However, adding to Renato Miotto's answer to this issue using xrandr as it fixed the problem for me. Here are some bash scripts that allow brightness control and can be mapped to the brightness keys. Hope they are helpful and save you some time.

https://github.com/AlexBV117/BashScreenBrightnessScripts.

1. Open a terminal with Ctrl+Alt+T.

2. Open the file /etc/default/grub from the terminal:

   sudo gedit /etc/default/grub
   

3. Update the following line from:

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" 
   

   to:

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=none"
   

4. Run from the terminal:

   sudo update-grub 
   

5. Restart the computer.

This worked for me. Ubuntu's own brightness control and keyboard brightness control work. Even when I turn the computer off and on, the setting does not change. This is real brightness control. When I lowered the brightness in third party programs, the screen became slightly bluish.